Money is one possibility. I'd also wonder if maybe it has something to do with being able to A) guarantee the cell count and B) guarantee viability.
And in reality, a starter would be necessary at a much lower gravity than 1.060. Unless your gravity is 1.028 or below, and your yeast is 96% viable (basically less than a few days old, it'll spend more than that in transit to the LHBS most of the time), you're going to need some form of starter for a 5 gallon batch if you want an optimal pitch rate. That said, if I'm brewing a beer 1.035 or below, I generally don't make a starter unless the yeast is fairly old. Anything else, I do.
